There are essentially two major groups of flexible foams which are of industrial significance. These are, on the one hand, flexible polyurethane foams and, on the other, latex foams. Both of these types of flexible foams have a similar range of uses.
Nonetheless, there are differences in production, starting points and mechanical properties between the two types of flexible foams.
Flexible latex foams thus have a somewhat different profile of the compressive strength curve as assessed by DIN 53 577 or ISO 3386, parts 1 and 2. The flexible latex foams do not exhibit a marked plateau in compressive strength, but, in comparison with flexible polyurethane foams, instead exhibit a continuous increase in compressive strength as compression increases.
It is precisely this property, i.e. a continuous increase in compressive strength as compression increases, which is desired for certain applications.
Thus, an object of the present invention was to influence the compressive strength/compression profile of flexible polyurethane foams in such a manner that behavior similar or identical to that of flexible latex foams is achieved. Another object was to produce flexible polyurethane foams wherein a mid-range compressive strength of between 2.5 and 4.0 kPa is achieved.
It has now been found that such a curve profile of flexible polyurethane foams may be established by polyol components of differing functionality, i.e. di- and more highly functional polyether polyols having a differing chain structure, without causing increased residual deformation of the foam. Moderate compressive strength values are achieved simultaneously at relatively high bulk densities.